Recovery of shale oil



June 23, 1970 J. T. PATTON RECOVERY OF SHALE OIL Filed Nov. 29, 1967 INVENTOR.

JOH N T- PATTON,

NEY.

w; no 2953005 29.252:

United States Patent O 3,516,495 RECOVERY OF SHALE OIL John T. Patton, Houston, Tex., assignor to Esso Research and Engineering Company Filed Nov. 29, 1967, Ser. No. 686,677 Int. Cl. E21b 43/24 U.S. Cl. 166-272 9 Claims ABSTRACT OF THE DISCLOSURE Shale oil is recovered from oil shale by injecting hot carbon dioxide into an undisturbed impermeable oil shale formation containing carbonates and having highly permeable water-bearing streaks to heat the formation and convert kerogen to shale oil which is recovered from a production well spaced from an injection well through which the hot carbon dioxide is injected.

BACKGROUND OF THE INVENTION Field of the invention The present invention is directed to recovery of shale oil. More particularly, the invention is concerned with recovery of shale oil by heating the oil shale in situ. In its more specific aspects, the invention is concerned with converting kerogen in oil shale to shale oil by injection of hot carbon dioxide.

Description of the prior art It is known to recover shale oil from oil shale by in situ combustion in which a mixture of inert gas and oxygen is injected into the oil shale to cause combustion in the oil shale and heat the formation. It is also known that oil shale formations are impermeable and fracturing of the formation is considered to be necessary. The use of critical ratios of carbon dioxide and oxygen in recovery of shale oil by in situ combustion is also known. Air has been injected into oil shale and in situ combustion initiated to recover shale oil with the hot combustion gases being forced to flow in a given direction to heat the formation. All these methods are open to disadvantages. For example, in situ combustion requires burning of part of the desired product. Likewise, heretofore, it was thought necessary to fracture oil shale prior to the combustion operation to allow the combustion products to penetrate the formation. It was not realized heretofore that the oil shale formation may be heated by injecting only hot carbon dioxide without a combustion operation and without prior fracturing of the formation followed by recovery of the shale oil.

Prior art considered with respect to this invention include the following listed U.S. Pats, 2,630,307, 2,841,375, and 2,877,847.

SUMMARY OF THE INVENTION The present invention may be briefly described and summarized as involving the recovery of shale oil by injecting into an oil shale formation hot carbon dioxide to heat the formation and convert the kerogen therein to shale oil which is then recovered.

The hot carbon dioxide may be suitably at a temperature within the range from about 600 to about 1800 F., preferably about 900 F. and may be injected at a rate from about 1,000,000 to about 3,000,000 cu. feet per day per surface acre, preferably about 2,000,000 cu. feet per day per surface acre.

The injection may continue for about 0.5 to about 2 years before first recovering oil, preferably about 1.0 to about 1.5 years, but continues, of course, during the life of shale oil recovery.

The injection is conducted through at least one injec- 3,516,495 Patented June 23, 1970 ice BRIEF DESCRIPTION OF THE DRAWING The present invention will be further described and illustrated with reference to the sole figure representing a preferred mode and embodiment.

DESCRIPTION OF THE PREFERRED MODE AND EMBODIMENT WITH RESPECT TO THE DRAW- ING Referring now to the drawing, numeral 11 designates generally a block of oil shale lands shown in cross section. The block of land 11 has drilled into it a plurality of injection wells 12 and production wells 13 which are both drilled to penetrate the oil shale zone '14 covered by overburden 15 and overlying zone 16.

Arranged on the surface 17 of block 11 is a furnace 18 provided with suitable heating means not shown and an oil and gas separator 19. Connected to furnace 18 is line 20 controlled by valve 21 leading to a source of carbon dioxide not shown. The source of carbon dioxide may suitably be facilities for generating carbon dioxide such as burning of fuel which may be oil shale, coal, or other carboniferous material. Leading from furnace 18 is a manifold 22 provided with lines 23 leading to the injection wells 12. Leading from the production wells 13 are lines 24 connecting into manifold 25 which in turn connects to oil and gas separator 19. Shale oil is recovered by line 26 from oil and gas separator 19 while carbon dioxide which is separated from the oil in separator 19 is withdrawn by line 27 controlled by valve 28 which connects into line 20 for recycle of carbon dioxide by line 20 to furnace 18. It may be desirable to provide suitable equipment to cool and condense any vaporous shale oil to allow separation from the carbon dioxide. Also, provision may be made for separation of other gases from the carbon dioxide before recycling the latter. In furnace 18 the carbon dioxide is heated to a temperature within the range of 600 to about 1200 F., and is injected into formation 14 through injection line 12. The hot carbon dioxide flows through the formation 14 in the direction shown by the arrows heating the formation and causing the kerogen in the formation to be converted to shale oil. The hot carbon dioxide, and vaporous and liquid shale oil flows into production lines 13 and thence by line 24 into manifold 25 and separator 19 for recovery by line 26. z I

Carbon dioxide is an improved heat carrier since it has a heat capacity of 12.4 B.t.u./ lb. mole/ F. Furthermore, carbon dioxide is stable at high temperatures and is quite soluble in the shale oil, and by virtue of solution in the shale oil lowers the viscosity of the shale oil and allows it to flow readily into the production wells 13.

Furthermore, carbon dioxide combines with carbonates in the rock matrix converting the carbonates to soluble bicarbonates in the presence of water, thus opening up channels through the oil shale formation and improving communication between wells. The carbon dioxide does not react with shale oil and is easily separated in oil and gas separators which are well known.

Heretofore, it has been supposed, because of the impermeability of oil shale formations, that it was always necessary to fracture the oil shale formation prior to recovery of oil shale by in situ combustion methods heretofore practiced. In accordance with the present invention, it has been discovered that oil shale formations contain highly permeable water bearing streaks. These water bearing streaks may comprise fractures, solution of nahcolite modules and beds, vugs, and breccia zones. The

porosity of the permeable water bearing streaks may be about 4 percent and thus does not significantly reduce the amount of kerogen in the oil shale. By virtue of the permeability of water bearing streaks, it is not necessary to fracture the formation and, by virtue of the solubility of carbon dioxide, the impermeability of oil shale is not an obstacle in in situ recovery of the oil shale in accordance with the present invention. In practicing the present invention, the hot carbon dioxide is injected under pressure at a temperature of about 900 F. to achieve desirable production rates. The carbon dioxide may be compressed by suitable compressors, preferably centrifugal, to the desired injection pressure and then passed through a furnace or heat exchanger to elevate it to the desired temperature. The pressure should be such that it is sufficient to inject the carbon dioxide but insufficient to fracture the formation.

The injection and production wells may be spaced apart horizontally and may comprise the so-called 5-spot or 7-spot arrangement. It is desirable to arrange the injection wells in the boundary of the perimeter of the area which is to be treated for recovery of the shale oil with the production wells arranged within the periphery such that the gases will travel towards the production wells and vaporized water and hydrocarbons will flow toward the production wells and not be lost.

In accordance with the present invention, the hot carbon dioxide is suitably injected at a temperature of about 900 F. and at a rate of about 2,000,000 cu. feet per day per surface acre of the area under treatment. The injection may continue for about 1.5 years before production of shale oil is initiated, but the injection continues during the life of the shale oil recovery with hot carbon dioxide and shale oil proceeding up the production well to surface and separated from the recovered shale oil and recycled. Some make-up carbon dioxide will be necessary and this amount may comprise about half of the injected carbon dioxide; lesser or greater amounts of makeup may be necessary.

The present invention is quite advantageous and useful in that higher recovery of valuable shale is possible without combustion and without fracturing operations, the sole medium used being the hot carbon dioxide.

The present invention has been described and illustrated by injection of hot carbon dioxide into an undisturbed oil shale formation. Thus, where mining has been practiced, large areas of exposed oil shale formation may be subjected to exposure to hot carbon dioxide.

It is important that hot carbon dioxide be employed in the present invention. Heat only will not allow obtaining the improved results nor will carbon dioxide only which is not heated generate permeability.

The nature and objects of the present invention having been completely described and illustrated and the best mode and embodiment contemplated set forth what I Wish to claim as new and useful and secure by Letters Patent is:

1. A method of recovering shale oil from an undisturbed impermeable oil shale formation containing carbonates and having highly permeable water bearing streaks which comprises:

injecting into said impermeable formation from the earths surface a sufficient amount of hot carbon dioxide for a sufficient length of time at a sufficient rate and at a pressure sufficient to force said hot carbon dioxide to move in contact with said water and carbonates through said formation but at a pressure insufiicient to fracture said formation to heat said formation and convert kerogen contained in said formation to shale oil and said carbonates to soluble bi-carbonates; and

recovering shale oil from said heated formation while continuing said injection.

2. A method in accordance with claim 1 in which the hot carbon dioxide is at a temperature within the range from about 600 F. to about 1800 F.

3. A method in accordance with claim 2 in which the temperature is about 900 F.

4. A method in accordance with claim 1 in which the injection rate is within the range from about 1,000,000 to about 3,000,000 cu. feet per day per acre.

5. A method in accordance with claim 4 in which the injection rate is about 2,000,000 on. feet per day per acre.

6. A method in accordance with claim 1 in which the hot carbon dioxide is injected into said formation for a time within the range from about 0.5 to about 2 years before first recovering shale oil from the heated formation.

7. A method in accordance with claim 6 in which the hot carbon dioxide is injected into said formation for a time within the range from about 1 to about 1.5 years before first recovering shale oil from the heated formation.

8. A mefhod in accordance with claim 1 in which the hot carbon dioxide is injected into said formation through at least one injection well and the shale oil is recovered through at least one spaced apart production well.

9. A method in accordance with claim 1 in which:

(a) the hot carbon dioxide is at a temperature within the range from about 600 F. to about 1800 F.;

(b) the injection rate is Within the range from about 1,000,000 to about 3,000,000 cu. feet per day per acre; and

(c) the hot carbon dioxide is injected into said formation for a time from about 0.5 to about 2 years hefore first recovering shale oil from the heated forma- OTHER REFERENCES Gary, Is Thermal Recovery the Answer to Economic 0 Production of Shale Oil? World Oil, vol. 161, No. 2,

Aug. 1, 1965 (pp. 98-101 relied on).

STEPHEN J. NOVOSAD, Primary Examiner 

